1. Field of the Invention
The invention relates to polypeptides and more particularly to the 38 kDa antigen of M. tuberculosis.
2. Brief Description of Related Art
Tuberculosis is a highly contagious human disease with over 3 million deaths and 8 million new cases occurring annually. The advent of AIDS is expected to worsen the situation because of reactivation of the dormant M. tuberculosis in immunocompromised individuals. The infectious dose in tuberculosis is exceedingly low, e. g. one to three tubercle bacilli are sufficient to initiate a primary lesion in the lung. The diagnosis of the infected individuals plays a vital role in the epidemiology and prevention and spread of the disease. Currently, diagnosis rests on the cultivation of M. tuberculosis from the sputum which takes about 6 weeks because of the slow growth rate of the organism. Another important part of the diagnosis is the `Tuberculin-test`. Tuberculin or the purified protein derivative (PPD) is a mixture of proteins from heat killed M. tuberculosis culture filtrate. This test suffers from high non-specificity due to cross-reactions in individuals infected with or vaccinated with other mycobacteria. Thus, there is an obvious need for developing defined and specific sero-diagnostic and skin-testing reagents for tuberculosis.
Serological studies have shown that the 38 kDa antigen of M. tuberculosis contains immunodominant epitopes specific to the virulent strains of M. tuberculosis. This antigen is produced in minor quantities in the vaccine strain BCG which is an avirulent derivative of the bovine-tubercle bacillus M. bovis. Thus, on the basis of serology, this antigen can be used to distinguish between organisms of M. tuberculosis complex and other mycobacteria. Purification of the native 38 kDa antigen directly from M. tuberculosis is not practicable because of the low yields, slow growth rates and the virulent nature of the organism.
As already stated, Mycobacterium tuberculosis is the causative agent of tuberculosis, a widespread human disease claiming about 3 million lives each year. Important goals of mycobacterial research are the provision of protective immunity against tuberculosis through more effective vaccines, and the development of specific skin-test/serodiagnostic reagents. A pre-requisite of such goals is the characterization and detailed evaluation of the immunological role of individual mycobacterial antigens. For this purpose, substantial amounts of such antigens are required. Purification of antigens directly from M. tuberculosis is difficult because of low cell yields, slow growth rates and the virulent nature of the organism (Kadival, G. V., S. D. Chaparas, and D. Hussong. 1987. Characterization of serologic and cell-mediated reactivity of a 38 kDa antigen isolated from Mycobacterium tuberculosis. J. Immunol. 139: 2447-2451. Young, D., L. Kent, A. Rees, J. Lamb, and J. Ivanyi. 1986. Immunological activity of a 38 kDa-kilodalton protein purified from Mycobacterium tuberculosis. Infect. Immun. 54: 177-183). A potential solution to this problem is the production of recombinant antigens in biotechnologically emanable organisms such as E. coli.
The immunological and diagnostic relevance of the 38 kDa protein antigen of M. tuberculosis has been shown previously (Andersen, A. B., Z.-L. Yuan, K. Haslov, B, Vergmann, and J. Bennedsen. 1986. Interspecies reactivity of five monoclonal antibodies to Mycobacterium tuberculosis as examined by immunoblotting and enzyme-linked immunosorbent assay. J. Clin. Microbiol. 23: 446-451; Young, D. et al. 1986. supra.). The protein contains species specific B-cell epitopes (Anderson, A. B. et al., supra.), and T-cells isolated from immunized mice, guinea pigs or humans proliferate when cultivated in its presence (Kadival, G. V. et al. 1987. supra.; Worsaae, A., L. Ljungqvist, K. Haslov, I. Heron, and J. Bennedsen. 1987. Allergenic and blastogenic reactivity of three antigens from Mycobacterium tuberculosis in sensitized guinea pigs. Infect. Immmun. 55: 2922-2927; Young, D. et al. 1986. supra.). The majority of humans (especially of the HLA type DR2), suffering from active tuberculosis develop antibodies against the 38 kDa antigen (Bothamley, G. H., J. S. Beck, G. M. T. Schreuder, J. D'Amaro, R. R. P. de Vries, T. Kardijito, and J. Ivanyi. 1989. Association of tuberculosis and Mycobacterium tuberculosis--specific antibody level with HLA. J. Infect. Dis. 19: 549-555).
The 38 kDa protein of the Gram positive bacterium Mycobacterium tuberculosis H37Rv is an immunodominant antigen of potential utility for diagnosis and vaccine development. Assessment of this potential requires large amounts of the purified protein that would be difficult if not impossible to obtain from M. tuberculosis itself.